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UWE Bristol Industrial Control UFMF6W-20-2

Control Systems Engineering UFMEUY-20-3

Lecture 1: Introduction to Control

Teaching

•  Course structure: –  1 hour lecture + 2 hour tutorial per week –  Two modules, co-taught (assessments are different) –  14 weeks control (Ben Drew & Neil Larsen) –  6 weeks sensors and actuators (Sabir Ghauri)

•  Tutorials: –  1st Semester: Classroom examples/problems –  Tutorial Sheets on Blackboard (and solutions) –  2nd Semester: Laboratory (Simulink, DC motor control

+ sensors and actuators) •  Lecture videos

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Assessment

•  1 coursework – laboratory report (40%) –  Group report

•  Exam after Easter Break (60%) •  Reading list:

–  The Art of Control Engineering, Ken Dutton, Steve Thompson, Bill Barraclough

–  Control Engineering, W. Bolton –  Control Systems Engineering, N.S. Nise –  Aircraft Control and Simulation, B.L. Stevens & F.L.

Lewis

Aims and Objectives

•  Control – System modelling – Transfer functions – System performance – System frequency response – System identification – Controller design

•  Sensors and Actuators

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Today’s Lecture

•  Introduction to Control •  Examples •  Control Basics •  Open- and Closed-loop control •  Control System Design Steps •  Example Models

Introduction to Control

•  What is a control system? •  Common example in the human body:

temperature control

Body%

Ac(on%

External temperature Sun, Illness, etc.

Body temperature

Sweat/shiver

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Introduction to Control

•  Applications in: – Physiology – Economics – Many fields of engineering:

•  Hydraulics •  Electronics •  Mechanics •  Etc.

Simple Examples

•  Car speed

•  Room fan

Thro-le% Engine%Desired speed Actual speed

Vehicle%

Actual cooling Switch% Wall%fan%Desired

cooling Electrical

power

System or Plant

Controller

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Examples

•  Control systems are required in complex machines, devices – Aircraft control systems – Anti-lock braking systems – Manufacturing processes

Examples

•  Inverted Pendulum – Demo

•  Videos – http://tinyurl.com/uwetriple – http://tinyurl.com/uweballrobot – http://tinyurl.com/uwebigdog – http://tinyurl.com/uwekestrel

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Control Basics

•  What is common for all these systems? •  A physical quantity has to be maintained at

a fixed value (or series of values) •  What information is necessary?

– What the system needs to do – How well is the system is doing – What control action keeps maintains the

action

Open and Closed Loop Control

•  Open Loop – Turntable example

DC%Amplifier%

Battery

Speed setting

DC motor

Speed

Turntable

Amplifier% DC%motor% Turntable%

Control%Device% Actuator% Process%Desired speed

(voltage) Actual speed

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•  Closed Loop

Open and Closed Loop Control

DC%Amplifier%

Battery

Speed setting

DC motor

Speed

Turntable

+ –

Tachometer

Amplifier% DC%motor% Turntable%

Control%Device% Actuator% Process%Desired speed (voltage) Actual speed +

–

Tachometer%

Sensor%

Error

Measured speed (voltage)

Open and Closed Loop Control

•  Cruise control example – Closed loop

– Output compared to the input – Error is used to drive the system

Thro-le% Engine%Desired speed

Actual speed

Speed%sensor%

Error

Feedback

+ –

Vehicle%

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Open and Closed Loop Control

•  Oven example – Closed loop

– Output compared to the input – Error is used to drive the system

Switch% Hea(ng%element%Desired temperature

Actual temperature

Temperature%sensor%

Error

Feedback

+ –

Electrical power

Open and Closed Loop Control

•  Components in a Closed Loop System

–  Normally depicted in a block diagram –  Plant provides the system output –  Controller takes the control input and provides a control output –  Sensor takes the output and feeds it to the subtractor (or comparator)

that compares the demand (the setpoint value) with the output of the sensor to produce an error

–  All connected by arrows, which represent signals

Controller% Plant%demand output

Sensor%

error

feedback

+ –

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Control System Design

•  Understand the general schemes that can be used to control a system.

•  Understand the system you’re trying to control. You need to predict how a system behaves – mathematical techniques that involve differential equation solution

Control System Design Steps

1.  System analysis – establish requirements (talk to users)

2.  Formal specification of required system performance

3.  System modelling – system must be accurately modelled before controller design can commence. Usually a differential equation (some quantity that changes w.r.t. time)

4.  Control algorithm development – the controller is developed using the model and standard control theory to meet the specifications.

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System Modelling

•  Dynamic behaviour of the system •  Linear or non-linear fashion •  System dynamics – how its output

changes in response to a particular input

Example

•  Furnace

•  The temperature of the furnace does not change instantaneously for changes in fuel rate

•  Differential equation describes the influence of time on the input response

•  Differential equations are derived from first principles

Furnace%Fuel flow rate (kg/s)

Temp (deg C) F θ

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Example models

•  Liquid level tank •  RC circuit •  Car suspension

Example 1: Liquid Level

•  Flow in – Flow out = rate of accumulation of liquid in the tank

Qin

Qout

h

C/S area = A

assume Qout= kh(k is a constant)

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Example 1: Liquid Level

•  Flow in – Flow out = rate of accumulation of liquid in the tank

Qin

Qout

h

C/S area = A

assume Qout= kh(k is a constant)

khdtdh

AQ

dtdh

AkhQ

dtdh

AQQ

in

in

outin

+=

=−

=−

First order differential equation

Example 2: RC circuit

•  Differential equation that related Vout to Vin

R

CVin Vout

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Example 2: RC circuit

•  Differential equation that related Vout to Vin

R

CVin Vout

dtdV

CRVV

RdtdV

CiRVV

outoutin

outoutin

+=

==−

dtdvCi = :currentCapacitor

Example 3: Car Suspension

•  Mass/spring/damper system

m

Fin

k D

xout

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Example 3: Car Suspension

•  Mass/spring/damper system

m

Fin

k D

xoutkxF

dtdx

DDvF

dtxd

MmaF

=

==

==

:Spring

:Damping

:Inertia 2

2

inout

inout

Fkxdtdx

Ddtxd

m

Fdtdx

Dkxdtxd

m

=++

+−−=

2

2

2

2

:Law Second sNewton' Applying

Today’s lecture

•  Control is an intrinsic part of humans and a vital part of many engineering systems

•  In order to control a system, we need to know the system/plant itself and control methods

•  Description of a system to be controlled – system model is a starting point of the control system design

•  Tutorial sheet 1: On blackboard. Determining differential equations for systems

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